"An average value for the thermal energy of coal is approximately 6150 kilowatt-hour (kWh)/ton."

22.14 GJ

Ever wondered how much energy you could get out of a ton of coal, but never
had the time to research it? Well, if you ever did, here's the answer
to your pondering. On average, a ton of coal produces 21 to 22 gigajoules
of energy.

The amount of energy produced by a ton of coal is largely dependent upon the
type of coal being burned. There are four major categories of coal, each differing
in composition and age. Lignite, also known as brown coal, is the least valuable
of the four. Lignite is primarily used as fuel for steam to generate electric
power. There is a compact form of lignite, called jet, which is sometimes used
as an ornamental stone. Sub-bituminous coal is the next in line in terms of
value. It is used primarily for electric power generation. Bituminous, a dense
dark brown to black coal, is also used primarily for electric power generation.
Substantial amounts of bituminous coal are also used for the production of coke,
a solid residue rich in carbon. The most valuable of the four, is the anthracite.
Anthracite is used for heating in residential and commercial buildings. The
higher cost of anthracite is due to its low content of impurities and high content
of carbon.

"Using an efficiency of 30% for transforming the heat energy of the coal into electrical energy and transmitting it to your light bulb (probably optimistic), we see that one pound of coal provides 4.11E6 Joules to your light bulb (I take 13,000 BTU/lb x 0.3 efficiency × 1054 Joules/cal) [sic. should be Joules/Btu -- Ed.]."

Did you know that coal can have as much energy per kg (if not more than) as
dynamite? Coal is an organic compound made up mostly of carbon but also has
small traces of hydrogen, nitrogen, sulfur and inorganic mineral compounds.
It is developed over millions of years from decaying plant and animal remains
under extreme pressure.

Coal is chiefly used as a fossil fuel but can also be used as a steel producing
agent, medicine, fertilizer, and pesticide. Coal can also be "coked"
which is the charring of coal originally intended to replace charcoal produced
from wood. Because of its sulfuric properties, Coal could not be used for food
nor alcohol production but was used in iron and steel production.

Coal is a mined product, and appears as a black or brown rock. Coal has
many forms including lignite (brown coal, is the lowest rank of coal and
used
almost
exclusively as fuel for steam-electric power) sub bituminous coal, bituminous
coal (a dense coal, usually black, sometimes dark brown used primarily
as fuel
in steam-electric power generation), and anthracite (anthracite is the
highest grade of coal, can yield double the energy that lignite can. Primarily
used
to heat residential and commercial establishments).When in its most efficient
state, coal can yield on the order of 3.2 × 1010 J
or 32 GJ.